KR101637450B1 - Boil-Off Gas Treatment System For Ship - Google Patents

Abstract

A system and method for treating an evaporative gas of a ship are disclosed. The present invention also provides an evaporative gas treatment system for a ship that stores and transports LNG with an LNG storage tank, comprising: a fuel tank storing LNG used as fuel for the ship; A compressor for compressing a boil-off gas generated in the LNG storage tank and an evaporative gas transferred when the LNG is unloaded to the outside of the ship; A fuel supply line connected to the fuel consuming destination of the ship from the downstream of the compressor and supplying the compressed evaporated gas as fuel; A re-liquefaction line for re-liquefying the evaporation gas, which is branched from the fuel supply line and supplied as fuel, to the evaporation gas to be introduced into the compressor by heat exchange with the evaporation gas to be stored in the LNG storage tank; And a gas separation line which is branched from the redistribution line and supplies the evaporated gas not re-liquefied to the lower portion of the fuel tank.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a boil-

[0001] The present invention relates to a system and a method for treating an evaporative gas of a ship, and more particularly, to a system and method for treating an evaporative gas of a ship, which comprises a boil- And the remaining amount is re-liquefied and stored, while the non-re-liquefied gas is injected into the lower portion of the fuel tank for processing.

In recent years, consumption of liquefied gas such as LNG (Liquefied Natural Gas) and LPG (Liquefied Petroleum Gas) has been rapidly increasing worldwide. The liquefied gas is transported in a gaseous state via land or sea gas piping, or is transported to a distant consumer site stored in a liquefied gas carrier in a liquefied state. Liquefied gas such as LNG or LPG is obtained by cooling natural gas or petroleum gas at a very low temperature (approximately -163 ° C. in the case of LNG), and its volume is significantly reduced compared to when it is in a gaseous state, .

The liquefied gas carrier, such as an LNG carrier, is used to load the liquefied gas with the liquefied gas and then to the sea to unload the liquefied gas to the onshore site. For this purpose, a storage tank capable of withstanding the extremely low temperature of the liquefied gas ).

Examples of maritime structures having storage tanks capable of storing liquefied gas at cryogenic temperatures include ships such as LNG RV (Regasification Vessel), LNG FSRU (Floating Storage and Regasification Unit), LNG FPSO (Floating, Production, Storage and Off-loading, and Barge Mounted Power Plant (BMPP).

In this specification, a vessel is a concept including a liquefied gas carrier such as an LNG carrier, a ship such as an LNG RV, and an offshore structure such as an LNG FPSO, an LNG FSRU, and a BMPP.

Since the liquefaction temperature of natural gas is a cryogenic temperature of about -163 ° C at normal pressure, LNG is evaporated even if its temperature is slightly higher than -163 ° C at normal pressure. For example, in the case of a conventional LNG carrier, the LNG storage tank of the LNG carrier is heat-treated, but since the external heat is continuously transferred to the LNG, LNG is transported by the LNG carrier, The LNG storage tank is constantly vaporized and boil-off gas (BOG) is generated in the LNG storage tank.

The generated evaporation gas increases the pressure in the storage tank and accelerates the flow of the liquefied gas in accordance with the shaking motion of the ship, which may cause a structural problem, so it is necessary to suppress the generation of the evaporation gas.

BACKGROUND ART [0002] Conventionally, in order to suppress and treat evaporation gas in a storage tank of a liquefied gas carrier, a method of discharging evaporation gas to the outside of the storage tank and incinerating it, a method of discharging evaporation gas to the outside of the storage tank, A method of returning to the storage tank after re-liquefying, a method of using evaporation gas as fuel used in a propulsion engine of the ship, a method of suppressing the generation of evaporation gas by keeping the internal pressure of the storage tank high, Have been used in combination.

In the case of a conventional ship equipped with an evaporation gas remelting device, the evaporation gas inside the storage tank is discharged to the outside of the storage tank and re-liquefied through the re-liquefaction device in order to maintain an appropriate pressure of the storage tank. At this time, the discharged evaporated gas is re-liquefied through a heat exchange with a refrigerant cooled at a cryogenic temperature, for example, nitrogen, mixed refrigerant, etc., in a liquefaction device including a refrigeration cycle, and then returned to the storage tank.

FIG. 1 schematically shows an evaporative gas treatment system of an LNG carrier equipped with a propulsion system using conventional LNG as fuel. As shown in FIG. 1, in this system, the evaporative gas compressor 10 and the heater 20 process the evaporative gas without installing the liquefaction facility, and then supply the evaporative gas to the propulsion system to consume the evaporative gas. However, in this case, when the amount of fuel required by the engine is less than the amount of evaporated gas, there is a problem that the evaporated gas is burned in a gas combustion unit (GCU) or sent to the vent mast 30 for venting .

As a result, there is a need to continuously research and develop systems and methods for efficiently treating liquefied gases, including evaporation gases that naturally occur from storage tanks.

In the case of re-liquefaction in order not to waste the evaporation gas generated in the storage tank, a refrigerant for re-liquefaction is required, and a refrigerant cycle should be provided. The provision of a separate refrigerant cycle has the problem of increased facility and operating costs and in-line space efficiency.

In view of this point, Japanese Patent Registration No. 10-1319364 discloses a technique of re-liquefying evaporated gas by using LNG supplied as fuel as a fuel in the case of a ship using LNG as fuel.

This technology does not require a separate refrigerant cycle to reduce equipment and operating costs, but has a problem that sufficient refrigerant can not be supplied to re-liquefy the evaporated gas when the LNG fuel consumption is low. Especially, a lot of evaporation gas is generated at the time of shipment of liquid cargo than at the time of ship operation, and there is a problem that it is difficult to process the evaporated gas because the ship does not generally propel the shipment and there is little or no consumption of LNG fuel.

Another technique is to provide the LNG storage tank as a pressure vessel and to hold the evaporation gas generated during the operation in the tank. However, in order to store a large amount of evaporated gas, the design pressure of the tank must be very high, so that the manufacturing cost of the storage tank rises and the economical efficiency deteriorates.

In particular, when LNG is loaded and unloaded from the LNG storage tank of the LNG carrier or the supply line to the outside of the ship, a large amount of evaporative gas is generated in the storage tank of the equipment receiving the LNG. And the evaporation gas is transported to the LNG carrier or the supply line. In this case, the amount of evaporative gas to be treated on the ship is further increased.

The present invention proposes a system and a method for efficiently and economically processing evaporative gas generated in a storage tank and evaporative gas returned from an unloading vessel while solving these problems.

According to an aspect of the present invention, there is provided an evaporative gas treatment system for a ship having an LNG storage tank for storing and transporting LNG,

A fuel tank for storing LNG used as fuel for the ship;

A compressor for compressing a boil-off gas generated in the LNG storage tank and an evaporative gas transferred when the LNG is unloaded to the outside of the ship;

A fuel supply line connected to the fuel consuming destination of the ship from the downstream of the compressor and supplying the compressed evaporated gas as fuel;

A re-liquefaction line for re-liquefying the evaporation gas, which is branched from the fuel supply line and supplied as fuel, to the evaporation gas to be introduced into the compressor by heat exchange with the evaporation gas to be stored in the LNG storage tank; And

And a gas separation line which is branched from the refilling line and supplies the unrefiltered evaporation gas to the lower portion of the fuel tank.

Preferably, the system further comprises: a re-liquidator provided in the re-liquefaction line for cooling the evaporated gas compressed in the compressor by heat exchange with a vapor to be introduced into the compressor; Liquid separator for supplying the LNG that has been re-liquefied through the re-liquidator and the expansion means to the gas-liquid separator for gas-liquid separation.

Preferably, the system further comprises: an evaporative gas supply line connected from the top of the LNG storage tank to the compressor; and an evaporative gas supply line connected from the fuel tank to the evaporative gas supply line for supplying evaporative gas generated in the fuel tank to the compressor A bunker line for unloading the LNG stored in the LNG storage tank to the outside of the vessel, and an evaporation gas generated when the LNG is unloaded through the bunkering line to supply the LNG to the evaporation gas supply line And may further include an evaporation gas return line.

Preferably, the system further includes a decompression device provided in the fuel gas supply line to decompress the evaporation gas generated in the fuel tank, wherein the fuel tank is provided as a pressure vessel, May be re-condensed by heat exchange with the LNG below the fuel tank.

Preferably, the refrigerator further comprises a cooler provided upstream of the re-liquefier in the refill liner and cooling the evaporated gas compressed in the compressor.

According to another aspect of the present invention, there is provided a method of treating an evaporative gas of a ship having an LNG storage tank and storing and conveying LNG,

1) compressing a boil-off gas generated in the LNG storage tank and an evaporative gas transferred when the LNG is unloaded to the outside of the ship;

2) supplying the compressed evaporated gas as fuel to a fuel consuming place of the ship;

3) cooling the remaining compressed evaporated gas supplied as fuel by heat exchange with the evaporated gas before compression; And

4) a step of gas-liquid separating the expanded evaporated gas after cooling to store the LNG in the liquid state as the LNG storage tank and supplying the gas to the lower part of the fuel tank where the LNG used as the fuel of the ship is stored; Is provided.

Preferably, when the amount of evaporative gas generated in the LNG storage tank is smaller than the required amount of fuel in the fuel consuming place of the ship, the LNG stored in the fuel tank and the evaporative gas generated in the fuel tank are supplied to the fuel consuming place .

The boil-off gas generated from the LNG storage tank and the evaporative gas returned when the LNG is unloaded from the ship are supplied as fuel for the in-vessel fuel consumption source in the ship's evaporative gas processing system of the present invention, The liquefied gas is injected into the lower portion of the fuel tank and processed. In particular, if the amount of evaporative gas generated in the LNG storage tank is less than the fuel requirement at the fuel consumption point of the ship, the LNG stored in the fuel tank and the evaporative gas generated in the fuel tank can be supplied to the fuel consuming place.

Through such a system, it is possible to supply a large amount of evaporated gas generated from the LNG storage tank of the ship and the returned evaporated gas as fuel to the fuel consuming place such as the inboard engine. In addition, when the amount of generated evaporation gas is large, some of the compressed evaporated gas after pressurizing is supplied as fuel to the fuel consuming place of the ship, and the remainder of the compressed evaporated gas is newly discharged or transported from the storage tank, It can be liquefied by cold heat and returned to the storage tank. As described above, the evaporation gas can be re-liquefied effectively without providing a separate refrigerant cycle, thereby reducing equipment and operation cost for re-liquefaction, contributing to the space inside the ship, and enhancing the transportation efficiency of the liquid cargo.

Especially, the un-liquefied gas is supplied to the lower part of the separate fuel tank made of the pressure vessel to dissolve in the LNG below the fuel tank so that the pressure rise is gentle and the pressure of the fuel tank is lowered. .

1 schematically shows an evaporative gas treatment system of an LNG carrier equipped with a propulsion system using conventional LNG as a fuel.
FIG. 2 schematically shows an evaporative gas treatment system for a ship in accordance with an embodiment of the present invention.

In order to fully understand the present invention, operational advantages of the present invention, and objects achieved by the practice of the present invention, reference should be made to the accompanying drawings and the accompanying drawings which illustrate preferred embodiments of the present invention.

Hereinafter, the present invention will be described in detail with reference to the preferred embodiments of the present invention with reference to the accompanying drawings. Like reference symbols in the drawings denote like elements.

2 schematically shows an evaporative gas treatment system of a vessel S according to an embodiment of the present invention.

2, the evaporative gas processing system of the present embodiment is an evaporative gas processing system of a vessel S provided with an LNG storage tank CT for storing and conveying LNG, A boil-off gas generated in the LNG storage tank CT and a compressor 100 for compressing the evaporated gas transported when the LNG is unloaded to the outside of the ship S A fuel supply line FL connected to the fuel consuming destination E of the ship S from the downstream of the compressor 100 and supplied with the compressed evaporative gas as fuel; A re-liquefaction line (RL) for cooling the remaining evaporation gas supplied to the compressor (100) by heat exchange with the evaporation gas to be introduced into the compressor (100) and storing the re-liquefied gas in the LNG storage tank (CT) And a gas fraction supplying the lower portion of the fuel tank (FT) And a liner (DL).

A vapor gas supply line BL is connected to the compressor 100 from an upper portion of the LNG storage tank CT and is connected to a fuel gas supply line FGL Is connected from the fuel tank FT to the evaporation gas supply line BL.

The LNG stored in the LNG storage tank CT is unloaded to the outside of the ship S along the bunkering line SL and transports the evaporation gas generated when the LNG is unloaded through the bunkering line SL, And the evaporation gas return line RTL for supplying the evaporated gas to the evaporation source line BL.

The ship S of this embodiment is a ship S that can store and transport LNG and supply it to the outside of the ship S, for example, an LNG carrier, an LNG supply line, and an LNG bunkering ship. The ship's exterior may be, for example, a terminal on the sea or onshore, or a vessel powered by LNG as fuel (LNG Fueled Ship, LFS). The LFS is equipped with a fuel storage tank (LFT) capable of receiving and storing LNG, but the LFS may not have a separate evaporative gas treatment system. When the LNG is unloaded to the LFS fuel storage tank, a large amount of evaporation gas is generated due to temperature and pressure changes. The evaporation gas generated during the bunkering can be returned to the bunker vessel supplied with LNG.

The propelling engine of the ship S is not driven during the unloading of the LNG, so that the amount of fuel required for the in-vessel fuel consuming destination E is small. However, since the amount of evaporative gas generated including the evaporated gas being conveyed may be large, The system re-liquefies the remaining evaporation gas supplied by the fuel and restores it in the LNG storage tank (CT), and supplies the un-liquefied gas to the fuel tank (FT) for future use as fuel.

On the other hand, the fuel consuming destination E of the ship S may be a facility for receiving the LNG as fuel, such as a propulsion engine for a ship S, a power generation engine, a gas turbine, and the like. For example, a DF engine (e.g., DFDG; Dual Fuel Diesel Generator) used as a fuel by mixing diesel oil and natural gas, an ME-GI engine supplied with high pressure gas of about 150 to 400 bara (absolute pressure), and the like.

When the amount of the evaporation gas generated in the storage tank and the amount of the evaporated gas to be returned is greater than the required amount of fuel in the in-vessel fuel consuming area E, the compressed evaporated gas is supplied to the fuel consuming area E through the fuel supply line FL And the remaining evaporated gas is re-liquefied through the re-liquefying line (RL) via the re-liquidator (200) and restored in the LNG storage tank (CT). When the amount of the evaporation gas generated in the storage tank and the amount of the evaporation gas to be returned are the same as the fuel required amount of the in-vessel fuel consuming entity (E), the entire amount of the compressed evaporation gas can be supplied to the fuel consuming destination (E) And supplies the LNG stored in the fuel tank (FT) and the evaporative gas generated therefrom to the fuel consuming destination (E).

In this embodiment, the fuel tank FT may be provided as a pressure vessel. The fuel gas supply line FGL is provided with a pressure reducing device 400 to reduce the pressure of the evaporation gas generated in the fuel tank FT and to join the evaporation gas supply line BL.

Meanwhile, the compressor 100 may be a multi-stage compression compressor 100 including a plurality of compression cylinders and an intercooler. The number of the compression cylinders and the number of the intercoolers may be determined depending on the fuel supply required pressure of the fuel consuming location E . For example, if the fuel consuming place E for supplying the gas is the ME-GI engine, the compressor 100 can be configured to compress the evaporation gas to 150 to 400 bar. The compressor 100 may have a structure in which a plurality of compressors are connected in series in addition to a structure in which a plurality of compression cylinders are arranged in one compressor 100.

The fuel supply line FL is branched at the intermediate stage of the compressor 100 to supply fuel to the fuel consuming area E at a relatively low fuel consumption point E such as DFDE, DFDG, gas turbine or the like at a fuel required pressure of about 5 to 50 bara, .

The re-liquefaction line (RL) is provided with a re-liquidator (200) for cooling the evaporated gas compressed by the compressor (100) by heat exchange with a vapor to be introduced into the compressor (100) The LNG that has been re-liquefied through the re-liquidator 200 and the expansion means 250 is introduced into the gas-liquid separator 300 to be gas-liquid separated.

As the temperature of the evaporation gas increases as it is compressed, it can be cooled by heat exchange with the evaporation gas that is generated in the LNG storage tank (CT) or conveyed from the LFS and compressed. Is supplied first to the fuel of the fuel consuming destination (E) at the rear end of the compressor (100) and the remaining amount is supplied to the re-liquidator (200) via the refueling line (RL). Therefore, since the flow rate of the evaporated gas before being compressed is larger than the flow rate of the compressed evaporated gas supplied to the re-liquidator 200 through the post-compression re-liquefaction line (RL), the compressed evaporated gas is cooled from the evaporated gas before being compressed And can be cooled and liquefied.

The fuel tank FT is provided as a pressure vessel and a pressure reducing device 400 is provided in the fuel gas supply line FGL so that the evaporation gas generated from the fuel tank FT is decompressed in the pressure reducing device 400, Can be joined to the evaporation gas supply line (BL).

A cooler 150 may be further provided upstream of the re-liquidator 200 in the re-liquefaction line RL to cool the evaporated gas compressed by the compressor 100 and supply the cooled liquid to the re- Although the cooler 150 is shown in FIG. 2 as being provided in the fuel supply line FL, the cooler 150 may be provided in the fuel supply line FL or the remelting line RL, if necessary.

An expansion means 250 is provided downstream of the re-liquidator 200 to allow the evaporation gas compressed and cooled while passing through the compressor 100, the cooler 150 and the re-liquidator 200 to be further cooled do.

The expansion means 250 may be provided as a pressure reducing valve, for example a line-thomson valve, or may be provided as an expander. The compressed and cooled evaporated gas is decompressed and liquefied while being thermally expanded in the expansion means (250), and introduced into the gas-liquid separator (300). Can be decompressed by the pressure of the fuel tank (FT) while passing through the expansion means (250).

A gas separation line DL is connected to the fuel tank FT from the upper portion of the gas-liquid separator 300 to supply the gas separated from the gas-liquid separator 300 to the lower portion of the fuel tank FT. At least a part of the gas supplied to the fuel tank FT through the gas separation line DL can be re-condensed while exchanging heat with the LNG under the fuel tank FT. The gas supplied to the fuel tank FT through the gas separation line DL is a cryogenic gas cooled through the re-liquidator 200, the expansion means 250 and the like even if it is not liquefied, ), The temperature and pressure inside the tank are not significantly increased. In addition, a part of the gas may be recycled through heat exchange with the LNG under the fuel tank (FT).

Particularly, when the gas is uniformly diffused from the lower portion of the fuel tank FT, the heat exchange with the LNG at the lower portion of the tank can be smoothly performed, the gas recondensation can be actively performed, and the increase in the internal pressure of the fuel tank FT can be made more smoothly, The safety of the tank can be ensured without increasing the design pressure of the fuel tank FT.

To this end, the end of the gas separation line DL may be provided so as to extend along the bottom or bottom of the fuel tank FT so as to distribute the gas to the lower portion of the fuel tank FT, or may be provided in the form of a porous pipe . It is also possible to provide a packing layer filled with a filler at the end of the gas separation line DL so as to increase the heat exchange time and the contact area of the LNG stored in the lower portion of the fuel tank FT.

As described above, in this embodiment, 1) compressing the boil-off gas generated in the LNG storage tank CT and the evaporative gas transported when the LNG is unloaded to the outside of the ship such as LFS; 2) while supplying the compressed evaporative gas as fuel to the fuel consuming place (E) such as the engine of the ship; 3) cooling the remaining compressed and supplied evaporated gas by heat exchange with the evaporated gas before compression; 4) The liquid phase LNG is stored in the LNG storage tank (CT), and the gas is supplied to the lower part of the fuel tank (FT) storing the LNG used as the fuel of the ship To treat the evaporated gas.

It is possible to supply a large amount of evaporative gas generated in the LNG storage tank (CT) of the ship S or in bunkering to the fuel consuming destination E such as the inboard engine, and when the amount of evaporated gas is large, By re-liquefying and storing by the cold heat of the evaporative gas itself without a cycle, the transportation efficiency can be improved and the on-board fuel supply can be smoothly performed.

In particular, by providing a separate fuel tank (FT) made of a pressure vessel, it is possible to smoothly supply the fuel even when the amount of generated evaporation gas is small and to supply the non-re-liquefied gas to the lower portion of the fuel tank (FT) The evaporation gas can be treated safely and economically while increasing the stability of the LNG storage tank (CT).

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Accordingly, such modifications or variations are intended to fall within the scope of the appended claims.

S: Ship
CT: LNG storage tank
FT: Fuel tank
E: Fuel Consumer
BL: Evaporative gas supply line
FGL: fuel gas supply line
RL: Re-liquefaction line
FL: fuel supply line
DL: gas separation line
100: Compressor
150: cooler
200: Re-liquidifier
250: Expansion means
300: gas-liquid separator
400: Pressure reducing device
LFS: Facilities outside the ship receiving LNG
LFT: Fuel storage tank
SL: Bunkering lines
RTL: Evaporative gas return line

Claims (7)

An evaporative gas treatment system for a ship in which an LNG storage tank is provided to store and transport LNG,
A fuel tank for storing LNG used as fuel for the ship;
A compressor for compressing a boil-off gas generated in the LNG storage tank and an evaporative gas transferred when the LNG is unloaded to the outside of the ship;
A fuel supply line connected to the fuel consuming destination of the ship from the downstream of the compressor and supplying the compressed evaporated gas as fuel;
A re-liquefaction line for re-liquefying the evaporation gas, which is branched from the fuel supply line and supplied as fuel, to the evaporation gas to be introduced into the compressor by heat exchange with the evaporation gas to be stored in the LNG storage tank; And
And a gas separation line for supplying an evaporated gas branched from the refill line and not refloated to the lower portion of the fuel tank. The method according to claim 1,
A re-liquefier provided in the re-liquefaction line and cooling the evaporated gas compressed in the compressor by heat exchange with a vapor to be introduced into the compressor;
Expanding means provided downstream of the re-liquidator for thermally expanding the compressed and cooled evaporated gas; And
And a gas-liquid separator for receiving the liquid-liquefied LNG through the re-liquidator and the expansion means and performing gas-liquid separation. 3. The method of claim 2,
An evaporation gas supply line connected to the compressor from an upper portion of the LNG storage tank;
A fuel gas supply line connected from the fuel tank to the evaporation gas supply line, for supplying evaporation gas generated in the fuel tank to the compressor;
A bunkering line for unloading the LNG stored in the LNG storage tank to the outside of the ship; And
And an evaporation gas return line for returning the evaporation gas generated when the LNG is unloaded through the bunkering line to the evaporation gas supply line. The method of claim 3,
Further comprising a decompression device provided in the fuel gas supply line for decompressing the evaporated gas generated in the fuel tank,
Wherein the fuel tank is provided as a pressure vessel and at least a part of the gas supplied to the fuel tank through the gas separation line is re-condensed by heat exchange with the LNG below the fuel tank. Evaporative gas treatment system. 3. The method of claim 2,
Further comprising a cooler provided upstream of said re-liquefier in said re-liquefaction line and cooling said evaporated gas compressed in said compressor. A method of treating an evaporative gas of a ship in which an LNG storage tank is provided to store and transport LNG,
1) compressing a boil-off gas generated in the LNG storage tank and an evaporative gas transferred when the LNG is unloaded to the outside of the ship;
2) supplying the compressed evaporated gas as fuel to a fuel consuming place of the ship;
3) cooling the remaining compressed evaporated gas supplied as fuel by heat exchange with the evaporated gas before compression; And
4) a step of gas-liquid separating the expanded evaporated gas after cooling to store the LNG in the liquid state as the LNG storage tank and supplying the gas to the lower part of the fuel tank where the LNG used as the fuel of the ship is stored; / RTI > The method according to claim 6,
And the LNG stored in the fuel tank and the evaporative gas generated in the fuel tank are supplied to the fuel consuming destination when the amount of the evaporative gas generated in the LNG storage tank is smaller than the required amount of fuel in the fuel consuming place of the ship Of the ship.

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